python batch reading of csv file

Question

I'm trying to do a batch reading of the csv file and process the batch by some callback.

import csv

with open('file.csv', 'r') as csvfile:
    reader = csv.reader(csvfile)
    header = next(reader) # skip header

    batch_size = 3
    batch = []
    count = 0

    for row in reader:
        if count >= batch_size:
            do_something(batch)
            batch = []
            count = 0

        batch.append(row)
        count += 1

Let's assume the CSV file has 10 rows (without a header), and a batch_size is 3 . The expected result should be 4 batches. 3 batches with 3 rows and the 4-th batch will only contain the 1 row. The code I wrote produces only 3 batches. If the batch size is 1/2/5/10 -- everything is ok.

Answer 1

Your condition count >= batch_size will not become True for the last few rows in case the number of rows cannot be divided by batch_size without producing a remainder.

Therefore, you need to manually clear the last batch / remainder. Just append something like this after the for loop:

if batch:
    do_something(batch)

This will call your function again, in case the last few rows have been accumulated into batch (which your loop already does, as it iterates over all rows available).